Download Unit 3B: The Brain Messing with the Brain Scientists can electrically

Unit 3B: The Brain
Messing with the Brain
 Scientists can electrically, chemically or magnetically stimulate parts of the brain and record effects
 Lesion: tissue destruction; naturally/experimentally caused destruction of brain tissue
Recording Brain’s Electrical Activity
 Tips of modern microelectrodes can detect electrical pulse in single neuron
Neuroimaging Technique
EEG (electroencephalogram)
CT scan/CAT scan (computed
tomography)
PET scan (positron emission
tomography)
MRI (magnetic resonance imaging)
fMRI (functional MRI)
Description
Amplified recording of waves of electrical activity across brain’s surface,
measured with electrodes on scalp
Takes x-ray photographs of brain at different angles
Visual display of brain activity that detects where radioactive form of glucose
goes when brain performs given task
Uses magnetic fields and radio waves to produce images of brain’s soft tissue
Reveals blood flow and thereby brain activity by comparing successive MRI
scans; shows brain function as well as structure
Brainstem (oldest part and central core of brain, responsible for automatic survival functions)
 Medulla: base of brainstem, controls heartbeat and breathing
 Pons: above medulla, helps coordinate movements
 Reticular formation: network of neurons extending from spinal cord to thalamus
o Filters incoming stimuli and relays important information to other parts of the brain and
o Involved in arousal
Thalamus (sits on top of brainstem)
 Receives information from all senses except smell
o Routes it to appropriate higher brain regions dealing with seeing, hearing, tasting, touching
 Receives replies from higher regions and directs it toward medulla and cerebellum
Cerebellum
 Judge time, modulate emotions, discriminate sounds/textures
 Coordinates voluntary movement (coordination)
Limbic System (neural system associated with emotions and drives, sits between older structures and cerebral cortex)
 Amygdala: influences aggression and fear including perception of them and processing of emotional memories
 Hypothalamus: regulates hunger, thirst, body temperature, sexual behavior
o “reward/pleasure center” - search and rescue rats made turns when directed using pleasure centers
o Reward deficiency syndrome: deficiency in natural brain systems for pleasure and well-being that leads
people to crave whatever provides that missing pleasure or relieves negative feelings (addiction)
Cerebral Cortex
 Cerebrum: two large hemispheres; make up 85% of brain’s weight; enables perceiving, thinking, speaking
 Cerebral cortex: surface layer of interconnected neural cells covering cerebrum
o Capabilities of learning and thinking increase as size of cerebral cortex increases
o Wrinkles in cerebral cortex decrease volume while increasing surface area
o Glial cells: provide nutrients and myelin, guide neural connections, clean up ions and neurotransmitters
 Located around neurons
 Capabilities of learning and thinking increase as number of glial cells increase
o Frontal lobe: behind forehead, involved in speaking, muscle movements, making plans and judgments
o Parietal lobe: top of head, receives sensory input for touch and body position
o Occipital love: back of head, receive information from visual fields
o Temporal lobe: side of head/above ears, receive auditory information from opposite ear
Motor Cortex (area at rear of frontal lobes that controls voluntary movements)
 Discovered by Fritsch and Hitzig
 Stimulating left/right hemisphere caused movements on opposite side of body
 Foerster and Penfield: movements with precise control require more cortical space
 Neural prosthetics: Monkey thinks about move, computer moves cursor with same proficiency as normal monkey
Sensory Functions
 Sensory cortex: area in parietal lobes that registers and processes body touch and movement sensations
o Discovered by Penfield
o More sensitive body region has more cortical area devoted to it in sensory cortex (lips = most sensitive!)
 Visual cortex: located in occipital lobes; receives visual information
o Visual information moves from occipital lobes to other area specialized in identifying words, detecting
emotions, recognizing faces
 Auditory cortex: located in temporal lobes; processes sound received from opposite ear
Association Areas (involved in higher mental functions like learning, remembering, thinking, speaking)
 Interpret, integrate, act on information processed by sensory areas
 Frontal lobes: judgment, planning, processing of new memories, moral judgment
o Phineas Gage: frontal lobes massively damaged, from friendly/soft-spoken to irritable/profane/dishonest
 Parietal lobes: mathematical and spatial reasoning
 Temporal lobes: recognition of faces
 Complex mental functions do not reside in one place
o Memory, language, attention result from synchronized activity among distinct brain areas
Language
 Aphasia: impairment of language; can be caused by damage to multiple different cortical areas
 Broca’s area: involved in speaking words, controls speech muscles via motor cortex
 Angular gyrus: involved in reading out loud, receives visual information and codes into auditory form
 Wernicke’s area: involved in hearing words, interprets auditory code
Specialization and integration
 Mind’s subsystems localized in particular brain regions yet brain acts as whole unit
 Brain divides mental functions (speaking, perceiving, thinking, remembering) into sub-functions
o Ex: breaks vision into color, depth, movement, form
 Continuous stream of experience is actually subdivided information processing occurring subconsciously
Brain’s Plasticity (ability to modify/fix itself after some types of damage)
 Some neural tissue can reorganize in response to damage
 Brain is most plastic during childhood
 Constraint-induced theory: rewire brain by restraining fully functioning limb and forcing use of “bad” limb
 Blindness/deafness makes unused brain areas available for other uses (better hearing/sight respectively)
 “phantom fingers”: people with lost hand feel someone sensation on hand when someone touches their arm; hand
cortex between face and arm; connections from arm invaded hand cortex to trigger both sensations together
 Neurogenesis: formation of new neurons; can happen in adults; increase by exercise, sleep and good environment
Splitting the Brain
 Corpus callosum: large band of neural fibers connecting and carrying messages between the two brain halves
o Vogel and Bogen separated brain hemispheres to cure extreme cases of epileptic seizures
 Split brain: the two brain hemispheres are isolated by cutting the corpus callosum connecting them
o Both hemispheres can comprehend and follow instructions simultaneously in split brain patients
 Gazzaniga’s experiments
o “heart” test: patients said they saw “art”, but pointed to “he” with left hand
o “spoon” test: seen in left field, patients could not say what they saw but could pick object with left hand
o Right hemisphere told to “walk”, left hemisphere came up with reason instead of saying “I don’t know”
 Left hemisphere: “interpreter”; constructs theories to explain people’s own behavior
 Information from left half of visual field goes to right brain hemisphere and vice versa
Right Brain Hemisphere
 Simple requests; quick, intuitive responses
 Perceiving objects, perceptual tasks
 Copying drawings
 Recognizing faces
 Perceiving/portraying emotions (damage disrupts
emotion processing and social conduct)
 Making inferences
 Sense of self (who you are, who your family is)
Left Brain Hemisphere
 Decisions, judgments
 Speaking
 Calculating
 Language
 Constructs theories to explain behaviors
Consciousness (awareness of ourselves and our environment)
 Evolutionary theory: consciousness must offer reproductive advantage
Cognitive Neuroscience (interdisciplinary study of brain activity linked with mental processes)
 Relates specific brain states to conscious experience; exploring/mapping conscious functions of cortex
 Some argue that conscious experience arises from specific neuron circuits firing in specific manner
 Others argue that conscious experiences produced by synchronized activity of whole brain
Dual Processing (most of brain works off stage)
 Information often simultaneously processed on separated conscious and unconscious tracks
Two-Track Mind
 Duality of vision
o Visual perception track: enables to recognize things and plan future actions
o Visual action track: guides moment to moment actions
 Hollow face illusion:
o Perceive hollow face as protruding but will wipe bug off inverted mask with accuracy
o Conscious mind does not know, but hand does
 Brain waves jump before conscious perception of decision to flick wrist which occurs before actual action
 Types of processing
o Unconscious processing occurs simultaneously on parallel tracks
o Conscious processing occurs serially; one thought/action after another